1. Field of the Invention
The present invention relates to a stepper motor control system. More particularly, it relates to a stepper motor control system adapted to drive a serial printer having a character printing wheel, space mechanism, and hammer mechanism, in which the stepper motor is rotated precisely by a desired amount of movement by controlling a change point between acceleration and deceleration when the amount of movement is smaller than a predetermined value.
2. Description of the Prior Art
The prior art publications in the field of the present invention are listed below.
a. Japanese Examined Patent Publication No. 32-8364;
b. Japanese Examined Patent Publication No. 39-27798 (filed Aug. 6, 1963, published Dec. 3, 1964);
c. British Patent No. 1112335 (filed Aug. 6, 1965, issued May 1, 1968);
d. FUJITSU, August 1968 "F462K/KI disc pack";
e. Japanese Unexamined Patent Publication No. 51-78638 (filed Dec. 23, 1974, open to public July 8, 1976);
f. Computer, September 1975 "IBM Line Printer"; and
g. Sogo Denshi Shuppansha, Feb. 10, 1979
In a conventional stepper motor control system, an acceleration table, a constant-velocity table, and a deceleration table are provided. To energize each phase of the stepper motor step by step, one of the above-mentioned tables is indexed to determine the phase to be energized, the electrical current to be supplied to the phase, and the period of time for the phase to be energized, as will be described later in detail with reference to FIG. 4. Using this conventional control, the stepper motor can be precisely controlled to be rotated by a desired amount of angular displacement and the rotor stops instantly at the desired target position only when the desired amount of angular displacement is greater than a predetermined value, so that the stepper motor is controlled by the acceleration table during acceleration, by the constant-velocity table during the constant-velocity period, and by the deceleration table during deceleration. This mode of control is referred to as a normal control mode. If, however, the desired amount of angular displacement is smaller than the above-mentioned predetermined value, the constant-velocity table is not used. That is, the stepper motor is controlled at first by a part of the acceleration table and then directly branched, without indexing to the constant velocity table, to an intermediate point of the deceleration table. This mode of control is referred to as a jump control mode. In this jump control mode the rotor of the stepper motor cannot stop instantly at the desired target position, because the acceleration table and the deceleration table are formed to meet the above-mentioned normal control mode, and the jump control mode is not taken into account. That is, in the jump control mode, a part of the acceleration table for the normal control mode is forced to be joined to a part of the deceleration table. The problem that the conventional jump control mode has stopping the load instantly will be described later in detail with reference to the drawings.
In order to stop the rotor of the stepper motor instantly when the desired amount of angular displacement is smaller than the predetermined value, an additional acceleration table providing a relatively small acceleration and an additional deceleration table providing a relatively small deceleration, are conventionally provided for controlling small amounts of movement (see Japanese Unexamined Patent Publication No. 51-78638). This countermeasure, however, causes an increase in the amount of hardware and requires complex control due to the additional acceleration and deceleration tables.